Fragment重叠问题

1：实例代码

    private void showFragment(int index){
        //开启事物
        FragmentTransaction transaction = manager.beginTransaction();
        hideFragment(transaction);
        switch (index) {
        case 0:
            if(fragment1 != null){//如过已经实例化，那么可直接显示出来
                transaction.show(fragment1);
            }else{//如果没有实例化，先实例化，在添加
                fragment1 = new TabFragment1();
                transaction.add(R.id.content, fragment1);
            }
            break;
        case 1:
            if(fragment2 != null){
                transaction.show(fragment2);
            }else{
                fragment2 = new TabFragment2();
                transaction.add(R.id.content, fragment2);
            }

            break;
        case 2:
            if(fragment3 != null){
                transaction.show(fragment3);
            }else{
                fragment3 = new TabFragment3();
                transaction.add(R.id.content, fragment3);
            }
            break;

        default:
            break;
        }
        transaction.commit();//切记要提交事物
    }

    /**
     * 隐藏所有的Fragment
     * @param ft
     */
    private void hideFragment(FragmentTransaction ft){
        if(fragment1 != null){
            ft.hide(fragment1);
        }
        if(fragment2 != null){
            ft.hide(fragment2);
        }
        if(fragment3 != null){
            ft.hide(fragment3);
        }

    }